#include <../src/vec/is/sf/impls/basic/gatherv/sfgatherv.h>

#define PetscSFPackGet_Gather PetscSFPackGet_Allgatherv

/* Reuse the type. The difference is some fields (i.e., displs, recvcounts) are not used in Gather, which is not a big deal */
typedef PetscSF_Allgatherv PetscSF_Gather;

PETSC_INTERN PetscErrorCode PetscSFBcastAndOpBegin_Gather(PetscSF sf,MPI_Datatype unit,PetscMemType rootmtype,const void *rootdata,PetscMemType leafmtype,void *leafdata,MPI_Op op)
{
  PetscErrorCode       ierr;
  PetscSFPack          link;
  PetscMPIInt          sendcount;
  MPI_Comm             comm;
  const void           *rootbuf_mpi; /* buffer used by MPI */
  void                 *leafbuf_mpi;
  PetscMemType         rootmtype_mpi,leafmtype_mpi;

  PetscFunctionBegin;
  ierr = PetscSFPackGet_Gather(sf,unit,rootmtype,rootdata,leafmtype,leafdata,&link);CHKERRQ(ierr);
  ierr = PetscObjectGetComm((PetscObject)sf,&comm);CHKERRQ(ierr);
  ierr = PetscMPIIntCast(sf->nroots,&sendcount);CHKERRQ(ierr);
  ierr = PetscSFBcastPrepareMPIBuffers_Allgatherv(sf,link,op,&rootmtype_mpi,&rootbuf_mpi,&leafmtype_mpi,&leafbuf_mpi);CHKERRQ(ierr);
  ierr = MPIU_Igather(rootbuf_mpi,sendcount,unit,leafbuf_mpi,sendcount,unit,0/*rank 0*/,comm,link->rootreqs[PETSCSF_ROOT2LEAF_BCAST][rootmtype_mpi]);CHKERRQ(ierr);
  PetscFunctionReturn(0);
}

static PetscErrorCode PetscSFReduceBegin_Gather(PetscSF sf,MPI_Datatype unit,PetscMemType leafmtype,const void *leafdata,PetscMemType rootmtype,void *rootdata,MPI_Op op)
{
  PetscErrorCode       ierr;
  PetscSFPack          link;
  PetscMPIInt          recvcount;
  MPI_Comm             comm;
  const void           *leafbuf_mpi;
  void                 *rootbuf_mpi;
  PetscMemType         leafmtype_mpi,rootmtype_mpi;

  PetscFunctionBegin;
  ierr = PetscSFPackGet_Gather(sf,unit,rootmtype,rootdata,leafmtype,leafdata,&link);CHKERRQ(ierr);
  ierr = PetscObjectGetComm((PetscObject)sf,&comm);CHKERRQ(ierr);
  ierr = PetscMPIIntCast(sf->nroots,&recvcount);CHKERRQ(ierr);
  ierr = PetscSFReducePrepareMPIBuffers_Gatherv(sf,link,op,&rootmtype_mpi,&rootbuf_mpi,&leafmtype_mpi,&leafbuf_mpi);CHKERRQ(ierr);
  ierr = MPIU_Iscatter(leafbuf_mpi,recvcount,unit,rootbuf_mpi,recvcount,unit,0/*rank 0*/,comm,link->rootreqs[PETSCSF_LEAF2ROOT_REDUCE][rootmtype_mpi]);CHKERRQ(ierr);
  PetscFunctionReturn(0);
}

PETSC_INTERN PetscErrorCode PetscSFCreate_Gather(PetscSF sf)
{
  PetscErrorCode  ierr;
  PetscSF_Gather  *dat = (PetscSF_Gather*)sf->data;

  PetscFunctionBegin;
  /* Inherit from Allgatherv */
  sf->ops->Reset           = PetscSFReset_Allgatherv;
  sf->ops->Destroy         = PetscSFDestroy_Allgatherv;
  sf->ops->GetGraph        = PetscSFGetGraph_Allgatherv;
  sf->ops->GetRootRanks    = PetscSFGetRootRanks_Allgatherv;
  sf->ops->GetLeafRanks    = PetscSFGetLeafRanks_Allgatherv;
  sf->ops->BcastAndOpEnd   = PetscSFBcastAndOpEnd_Allgatherv;
  sf->ops->ReduceEnd       = PetscSFReduceEnd_Allgatherv;
  sf->ops->FetchAndOpEnd   = PetscSFFetchAndOpEnd_Allgatherv;
  sf->ops->CreateLocalSF   = PetscSFCreateLocalSF_Allgatherv;

  /* Inherit from Gatherv */
  sf->ops->FetchAndOpBegin = PetscSFFetchAndOpBegin_Gatherv;

  /* Gather stuff */
  sf->ops->BcastAndOpBegin = PetscSFBcastAndOpBegin_Gather;
  sf->ops->ReduceBegin     = PetscSFReduceBegin_Gather;

  ierr     = PetscNewLog(sf,&dat);CHKERRQ(ierr);
  sf->data = (void*)dat;
  PetscFunctionReturn(0);
}